Computational study of the decomposition mechanisms of ammonium dinitramide in the gas phase

Abstract

<p>CBS-QB3 method has been employed to determine the geometries, the vibrational frequencies of the reactants, the products and the transition states involved in intramolecular hydrogen-transfer and decomposition reactions of the free gas-phase H₃N···HN(NO₂)₂ (ADN^*). The results show that the intramolecular hydrogen-transfer reaction of ADN^* is more feasible than that of HDN. ADN^* and its hydrogen-transfer isomers ADN^*-IIa,b,c decompose along four channels to form NH₃ + HONO + 2NO (P_I), ȮH + ṄO₃ + N₂ + NH₃ (P_II), ȮH + ṄO₂ + N₂O + NH₃ (P_III), and HNO₃ + N₂O + NH₃ (P_IV), respectively. It has been found that the dominant decomposition channels are P_I and P_III. The hydrogen-transfer reaction can reduce the barrier of elimination of NO₂ and forming N₂O reactions in ADN^* and HDN. The decomposition of ADN^*-IIc to form NO₂ and N₂O is more feasible than that of the gas-phase HDN. The rate constants (<i>k</i>) of rate-determining step of ADN^* show that <i>k</i>_PI and <i>k</i>_PIII are higher than <i>k</i>_PIV and <i>k</i>_PII. Compared with HDN-IIc → N₂O+ȮH+ṄO₂, <i>k</i>_PIII of ADN^*-IIc is significantly higher than that of <i>k</i>^HDN-IIc. These results reveal that NH₃ (as a chaperon) has a certain influence on the decomposition mechanisms and kinetics of ADN^*.</p